Abrasive article and method of making



All@ 6,1946 D. B. sHARFE: E-rAL 2,405,524

ABRASIVE ARTICLE AND METHOD 0F MAKING' Filed June 27 1944 Patented Aug.6, 1946 ABRASWE ARTICLE AND METHOD OF MAKING Donald B. Sharpe, NorthTonawanda, and Richard A. Baumgartncr,'Niagara Falls, N. Y., assignorsto The Carhorundum Company, Niagara Falls, N. Y., a corporation ofDelaware Application June 27, 1944, Serial No. 542,325

This invention relates to the manufacture ci abrasive articles. Moreparticularly, it relates to the manufacture of resilient abrasivearticles of the bonded type 'such as grinding and polishing Wheels,stones, discs, blocks, pads, sticks and the like formed of a compositeof felted, fibrous sheets having abrasive grain, and usually an adhesivebinder therefor, included internally of the fibrous sheets. Theinvention especially pertains to the making of such articles from aplurality of superimposed flexible, fibrous, abrasive-containing sheetsof web material whereby the individual abrasive-included sheets arecombined by means of an adhesive such that the iinished article retainssubstantially all the softness of cutting or polishing behavior inherentin the abrasive-included fibrous sheet material constituting theabrasive body, and at the same time the abrasive article possesses anincreased cutting rate over that normally expected or found in suchproducts.

There has always been a need for abrasive articles of the bonded typewhich would combine an effective cutting action with satisfactorynishing or polishing whereby a reasonable amount of material would beremoved from the work be. ing abraded and at the same time the articlewould be left with a desirable surface nish or polish. Abrasive articlesheretofore provided for such dual purposes have not been completelysatisfactory in accomplishing both goals and have been found to bedeficient in one respect or another. Among the reasons for theirunsatisfactoriness have been the failure to combine an appreciabledegree of cutting ability "with a resilience or softness of ,cuttingaction, nonhomogeneity of the abrasive article, lack of permanency ofthe abrasive content (i. e., failure of the abrasive wheel structure toretain the abrasive particles within the abrading body), non-uniformityof abrasive action, infiexibillty, etc. Provision of satisfactoryproperties in one respect has usually been at a 'sacrifice of one ormore of the other characteristics desirable in such products. i

In the past, attempts have been made to obtain the desired combinationof cutting and polishing by incorporating fibrous llers in `moldedabrasive articles such as articles made with a rubber bond. Theseproducts have not been satisfactory and none of them has ever beencommercialized to any material extent.

In the recent past, an entirely new type of abrasive article has beendeveloped which has gone into widespread commercial use. These ar- 9Claims. (Cl. 51--193) ticles and methods of making them are described indetail in copending application Serial No. 408,935, filed August 30,1941, issued on August l5, 1944, as U. S. Patent No. 2,355,667. They aremade by rst preparing sheet material which contains a Very substantialamount of abrasive grain included throughout the body of the material.The base of the sheet material is usually staple length cotton fibersand the sheets are made by any of several processes, as Will bedescribed in more detail hereinafter. In addition to a Inechanicalinterlocking of the fibers and retention of the grain by suchinterlocking, the sheet material is usually provided with an adhesivewhich is incorporated during the manufacture of the Iwebs from which thesheets are cut. Adhesives of various types may be employed, one commonone being a mixture of rubber and casein. The sheets vary in thickness,being generally of the order of .010 inch.

According to the invention of application Serial No, 408,936, abrasivearticles such as wheels, stones, sticks, and the like are lformed fromthe sheet material by assembling a number of such sheets to formarticles of the desired thickness. In making such articles the adhesivewhich is present in the sheet material may be wholly relied on forbonding the sheets together or additional adhesive may be applied to vbonded materials being commonly referred to as "s0ft while the wheels inwhich the abrasive grains are more firmly bonded, as by the use oflarger quantities of bonding material, are referred to as hard It hasalso been found that articles of different grade are required in thefield in which the abrasive wheels made from the sheet material areused. By following the teachings of application Serial No. 408,936, ithas been possible to make a variety of grades of the softer1 typewheels, but until the development of the present invention satisfactorywheels of this kind in the harder grades have never been made.

One method described in the earlier-filed application which has beentried unsuccessfully in an attempt to make the harder type of wheels hasbeen through the use of the stronger and heatresistant type of bondssuch as phenol-aldehyde condensation products. According to theearlierwfiled application, such bonds may be used but the methodstherein described for incorporating such resins have made articles'whichare not wholly satisfactory. For example, if the phenolic resin isemployed in the form of either a liquid resin or a solution of solidresin in a suitable solvent the resins penetrate the sheet material andmaterially reduce the resilience found in articles using more flexiblebonds. As a result the abrasive Wheels thus made do not have thecharacteristic resilience and other combinations of unusual propertiesfound in Wheels of this type Where other adhesives are used.

We have discovered that Wheels which have both a higher cutting rate anda longer abrading life than articles of the prior application can bemade by employing as an adhesive for joining the sheet material aphenol-aldehyde condensation product modified in such a way that theliquid is substantially non-penetrative, at least to the extent that itdoes not saturate and impregnate the 'sheet material as is the case withthe resins of the earlier-filed application. As a consequence We havefound that wheels made in accordance with our invention retain to aconsiderable extent the resilience and polishing action of the Wheels ofthe earlier-Filed application and at the same time have a much highercutting rate anda longer life.

We have also discovered that the characteristics of the abrasivearticles made in accordance with our invention can be modified to someextent by the employment of various fillers, the grade of the articlebeing determined to some extent by the particular ller selected as Wellas by the nature of the adhesive.

The adhesives used in our invention are fundamentally mixtures ofWater-miscible liquid phenolic resins with water. Such mixtures may beused alone or powdered, normally solid resin may be suspended in suchmixture and, as stated, inert filler may also be employed to modify thecharacter of the finished Wheel.

When such adhesive compositions are applied tothe surface of fibrousmaterial the resin and the filler are retained upon or adjacent thesurface of the fibrous sheet and the loss of the Water of the adhesivecomposition by absorption into the fibrous structure and by evaporationserves to raise the viscosity of the composition to the point where theresin does not soak into the fibrous material. At the same time theresin and filler on curing provides the abrasive article with a greateroverall hardness which greatly enhances the cutting ability withoutdetracting from the softness characteristic of the iibrous, abrasivefincluded structure. The combining phenolic adhesive composition isapplied to one or both sides of the abrasive-included, fibrous sheetmaterial and can be applied while the material is in roll form, after ithas been cut in the form of large sheets, or after it has been cut tothe ultimate size and shape to be used in fabricating the iinal abrasivearticle,

After the abrasive-included, fibrous sheet material has been properlysized, as above described, it is out to the desired size and shape and asuitable number of the sheets are assembled in superimposed relation andconsolidated as by heat and pressure to form the desired article. Theformed article is then usually given a further oven cure to complete thecuring of the phenolic binder whereupon the abrasive article is edgedand dressed according to standard practice and the article is ready foruse.

In order to better understand the nature of the d invention, referenceis made to the accompanying drawing, in which:

Figure 1 is atop plan View of an abrasive grinding Wheel made inaccordance with the present invention;

Figure 2 is a vertical diagrammatic crosssection through the line II-IIof Figure l; and

Figure 3 is a highly enlarged, fragmentary section of Figure 2.

The abrasive-included, rlbrous web material used in making the productsof the present invention can be manufactured in several Ways. A verysatisfactory method of making includedabrasive sheet material of theherein required type is that set forth and fully described in U. S.Patents Nos. 2,284,715 and 2,284,716. Briefly, the felted fibrous web isformed by feeding a plurality of thin carded fibrous membranes from anumber of carding assemblies onto a moving endless support so that eachmembrane is deposited or superimposed upon the preceding membranes untila web of loosely felted fibrous material of the desired thickness isbuilt up on the traveling Support. A number of abrasive grain hoppersare also disposed between the carding assemblies and above the travelingconveyor. Abrasive grain is fed from the hoppers onto the brousmembranes at various stages in the building up of the final web, sothat, as a result, the abrasive material is applied between theindividual membranes making up the web and so is internally distributedthroughout the brous web or sheet. A suitable adhesive binder is thenincorporated within the fibrous-abrasive web and the Web is consolidatedto a desired density and passed to a curing zone, Where the adhesive ismatured or set. The included-abrasive web is then Wound into rolls foruse as a source material for the manufacture of the products hereindescribed.

In practicing the invention, any of the abrasive materials in common usemay be employed, such as silicon carbide, diamonds, boron carbide, fusedaluminum oxide, iiint, corundum, emery, rouge and similar substances.The size of the abrasive particles may vary from the finest polishing orbuiiing powders to the coarser grit sizes used in grinding.

Other methods of incorporating abrasive material internally of the broussheet material during its manufacture may be employed. VFor example, theabrasive particles can be thoroughly admixed with the adhesive binderand the mixture applied to the uncompacted web by the usualadhesive-applying rolls. This method has been found to be particularlysatisfactory for the inclusion of the ner abrasive materials of the sizeemployed in bufiing and polishing operations.

Another method is to project the abrasive material into the web 0r sheetafter it has been built up to the desired thickness and immediatelyprior ,to consolidating the web. The projection of grain is suitablycarried out by means of a blast of air or gas against one or bothsurfaces of the fibrous web, the air stream being laden with theabrasive material to be included internally of the web. The other stepsin the formation and consolidation of the web are carried out in amanner similar to that used in the previous procedures.

Felted brous Webs having abrasive material included Within the web andwhich are suitable for use in the fabrication cf the herein describedproducts can also be made by a modification of the above processes inwhich the individual fibers are interwoven and interlocked by a gentleair or gaseous agitation of the thin carded membranes during theirdeposition. This process is termed aerodynamic weaving and is used topromote the strength and eliminate any laminations from the web. For amore complete description of such a process and product, reference ismade to U. S. Patents Nos. 2,284,738 and 2,284,739 in which furtherdetails are also given of the above procedures for including abrasivematerials within the fibrous structures.

Abrasive sheet material of the herein required type can also be made bywet felting procedures employing the various types of paper-stock fibersand including abrasive therein at the time of making the sheet material.One satisfactory method of making the ab-rasive-included sheet materialby wet felting procedure is that set forth and fully described incopending application Serial No. 461,139, filed October '7, 1942.

Briefly, the felted fibrous paper stock material having abrasive grainincorporated internally thereof is made by first forming a liquid,usually aqueous, suspension of fibrous material, the fiber content ofthe suspension being very low and in 'the neighborhood of 0.5 to 5% ofthe suspension, collecting the fibrous suspension on a suitable support,introducing abrasive grains with or without an adhesive binder into thefibrous web while it is in a highly aqueous, or fluid, condition,extracting the water or other liquid medium from the web, and furtherdrying and compacting the` web to the desiredv density. Optionally, theabrasive gra-ins can be given a p-reliminary coating of a suitableadhesive, which is preferably soluble or softenable in the liquidsuspending medium or a component thereof, to assist in holding thefibrous abrasive-containing web in compacted form after it has beencompressed. The process can be carried out in a number of ways.

In one such modification the fibrous suspension of paper-stock isdeposited upon a foraminous support in one step and the abrasive grainis deposited in several increments while the web is still inV a' highlyaqueous or fluid condition. That portion of abrasive applied firstpenetrates deepest into the web structure, and the abrasive of eachsucceeding deposition penetrates the web to a lesser degree by reason ofthe continually decreasing amount of water present and the consequentthickening of the fibrous body. The distribution of abrasive Within theweb can thus be controlled by variation of the amounts and places ofdeposition during the dewatering of the web so as to obtain any desiredeffect.

In a modified form of the process a fiuid fibrous suspension iscollected upon a plurality of revolving foraminous supports, such ascylinders, which are partially immersed in the fibrous suspension. Thethin fibrous membranes collected upon the foraminous supports are thensuccessively transferred to a common carrier, usually a moving endlessfelt blanket or belt, in superimposed relationship to form a fibrous webstructure. Abrasive grain is incorporated into the fibrous web structureby deposition or projection between and into the various individualmembranes as they are deposited 0n the carrier support. This method hasthe advantage that, since the fibrous suspensions can be varied, thecomposition or structure of various portions of the web can be varied ifdesired. Adhesive binders can be incorporated in the fibrous web,regardless of the procedure used, at various stages in the process, suchas by inclusion in the fibrous suspension, introduction duringdewatering of the web, with the abrasive grains as a coating there- Gis6 on, or after the web has been substantially de watered and prior tothe final compacting and drying of the web.

A still further modification which can be used to make fibrous abrasivematerials is the process of forming a wet fibrous abrasive lap by acylinder wet-press process, in which a fibrous suspension similar tothat used in the cylinder method above is fed, usually from a singlecylinder mold, onto a traveling wet felt carrier belt. The thin brousmembrane is conveyed over one or more suction boxes to remove a portionof the water and passed between a pair of pressure rolls. As the b-rousmaterial passes between the pressure rolls it is transferred to theupper pressure roll upon which it is wound in a series of successivelayers until the desired thickness of fibrous material is obtained,whereupon the material is removed by hand or by a suitable knife ordoctor blade. Abrasive grain is fed onto the brous sheet previous to itspassage between the pressure rolls and is thereby incorporated withinthe fibrous structure.

Another satisfactory method of making included-abrasive, paper-stock webmaterial is that set forth and fully described in copending applicationSerial No. 461,140, filed October 7, 1942. In accordance with theprocess therein set forth, fibrous paper-stock abrasive sheet materialis made from an aqueous suspension of around 3% fiber content in whichthe fibers are distributed in the suspension as substantiallyindividually separated fibers. This fibrous suspension is agitated,beaten, or otherwise mechanically treated, with sufficient vigor torender the fibers partially gelatinous, abrasive grain beingincorporated in the suspension to the desired extent. A sufficientamount of abrasive grain is added to provide an abrasive grain contentof over 40%, and preferably -'70% or more by weight of the final productafter the water has been extracted. Thek agitation of the fibroussuspension previous to and/or during the addition of abrasive grain` isvery important in preparing a liquid in which the abrasive particleswill remain uniformly in suspension. This stability of suspension isbelieved to be due, at least in part, to the adherence of the abrasiveparticles to the partially gelatinized fibers. The amount of agitationor beating of the fibrous suspension necessary to provide a suitablestable mixture of abrasive and fiber of the proper consistency dependsupon the size of the abrasive particlesA For example, a very slightagitation serves the purpose when the finest abrasive polishing powdersare used whereas with the use of 60 or 80 grit abrasive grains, it isdesirable to subject the suspension to a much longer and/or vigorousagitation. Suspension of the abrasive particles may be assisted byincorporating an adhesive in the uid mass, either in the form of apreliminary coating of the abrasive particles or by the addition of theadhesive to the liquid. In either case, the adhesive should preferablybe soluble in the liquid medium of the suspension or at least softenableor. soluble in a component thereof.

After a fiber-abrasive suspension of suitable consistency has beenprepared as above outlined, it is flowed or otherwise deposited on asuitable n s foraminous support in the form of a continuous,

highly aqueous layer from which the water or other liquid suspendingmedium is extracted, and the resulting film is further dried andcompacted to the desired density. These operations can be performed byflowing the suspension onto a moving endless wire screen or bycollecting a plurality of thin membranes onto cylinder molds andtransferring them to a suitable felt blanket in superimposed relation toform a web of the desired thickness. While it is usually desirable toproceed in the described manner of forming continuous fibrous webs bythis particular method, the process can be practiced in modified form byusing the same thin suspension of bers and abrasive to form individualabrasive-included sheets by a series of discontinuous steps. Adhesivebinders can be incorporated in the fibrous web, regardless of theprocedure used, at various stages in the process, such as by inclusionin the fibrous suspension, introduction during dewatering of the web, asa coating on the abrasive grains, or after the web has beensubstantially dewatered and prior to the final compacting and drying ofthe web.

Modifying agents such as waterproofing compounds, anti-friction agents,exibilizers, plasticizers and other fillers may be incorporated in theweb at the time of making irrespective of the particular procedurefollowed, in order to render the web resistant to water or impart otherspecic desirable properties to all or certain controlled portions of theweb.

Abrasive-included, fleted fibrous web material such as that made by anyone of the aforementioned methods is used as a source of raw materialfor the making of abrasive articles in accordance with the presentinvention. As a specific example of the manner in which the presentprocess has been carried out and an abrasive article made in accordancewith the present invention, the following procedure is given.

A eXible, felted fibrous web material made in accordance with theteachings of U. S. Patents Nos. 2,284,738 and 2,284,739 containingapproximately 75% of fused alumina particles of 80 mesh grit size,cotton ii'oers and 10% rubber material derived from latex, is sized withan aqueous solution of a water miscible phenolic resin containing finelydivided inorganic cryolite llers to provide about wet weight of coatingmaterial basedV on the weight of the fibrous sheet material. Acomposition which has been found highly satisfactory for the purpose ofapplying as an adhesive sizing coating to one or both sides of thefibrous sheet material is the following:

Sizing composition No. 1

Parts by Weight Water-miscible, liquid phenolic resin (such as thatknown and sold under the trade name Bakelite BR 10190) 45.0 Powderedcryolite 31.5 WaterY 23.5

The phenolic resin hereinabove specified is only given as a specificexample of one type of nonpenetrative phenolic resin which has beenfound highly adaptable for use in carrying out the present invention. Itis a liquid phenolic resin which is miscible with water, at least to alimited degree, to form a clear solution, and by reason of the aqueousnature of the resin solution as herein used, does not penetrate thefibrous backing to an undesirable degree. Other non-penetrating phenolicresins can be provided by forming a dispersion or an emulsion of a solidand/or liquid phenolic resin in water in which case on application ofthe sizing adhesive to the ibrous web material the water constituent ofthe composition tends to penetrate the brous structure, whereupon theresinous component remaining becomes vau so viscous that it does notpenetratethe fibrous web but remains substantially on the surface.Retention of the resin on or adjacent the surface during curing of theresin is further accomplished by employing a water-miscible resincontaining a minor amount of a solid resin. During the initial curingstage when the liquid resin would normally fall to a lower viscositywhereby it might penetrate the fibers, the solid resin simultaneouslydissolves in the liquid resin so as to raise the viscosity of the latteror at least maintain its original viscosity so as t0 retard or preventpenetration. A resin composition of this latter type found suitable forthe herein proposed use and containing a nller is as follows:

Sizing composition No. 2

Parts by weight Liquid phenolic resin (such as that known and sold underthe tra-de name Bakelite BR 10190) 40.9 Solid powder resin (such as thatknown and sold under the trade name Bakelite BR- 2417) 9.1 Cryoliteiiller 28.6 Water 21.4

Although cryolite has been specified as the filler in both of theadhesive sizing compositions given above, other inorganic fillermaterials can be used. For example, satisfactory results are obtained bythe use as llers of such substances as Whiting, various clays and otherfinely divided mineral fillers.

After applying an adhesive size or coating composition such as sizingcomposition No. 1 above, the adhesively sized fibrous material is driedat about F. for approximately 30 minutes, whereupon it is ready forimmediate further processing, although the sized and dried materialretains sufficient tack that it can be set aside and further processedafter storage for several weeks.

The dried, resin-coated material is then cut to the desired size andshape for use in making the abrasive article. For example, in making thegrinding wheel illustrated in the drawings a number of disc-shapedpieces of sheet material having the diameter` of the wheel shown inFigure 1 are out from the web material and assembled in superimposedrelation to form the abrasive wheel. Instead of sizing the abrasive webmaterial in roll form prior to cutting to size, the web can be sizedwith the desired adhesive after it has been cut to size, although theformer method is preferred because of the greater facility of sizing anddrying the material in roll form. Also, in forming abrasive wheelshaving a central mounting arbor, the arbor hole can be cut from theindividual disc-shaped pieces at the time of cutting the web material orcut from the formed article after the disc-shaped sheets have beencompressed, depending upon the thickness of the wheel being made.

More recently, improved methods of reducing the web material in sizedcondition to the ultimate size for use in forming the nal abrasivebodies of the desired shape have been devised. These improved methodshave been more fully set forth and described in the copending applica-`tion Serial No. 542,324 led June 27, 1944, issued on May 8, 1945, as U.S. Patent No. 2,375,263; they are applicable to carrying out the presentinvention and in fact constitute the preferred method of performing theadhesive-applying and cutting of the web material. Brieiiy, theabrasive-included, fibrous web material isf'rst sized with a suitablewater-miscible, phenolic resin composition such as that given in Example1 above, either in roll form or in the shape of relatively large sheetsof the material, after which a sufcient number of large sheets of theadhesively-coated material are assembled in superimposed relation toprovide a slab of specied thickness, as for example, Mi thick whencompressed as by cold-pressing at approximately 4000 pounds per squareinch. The number of individual sheets to be used in forming one of thecompacted slabs is determined by weighing. In the case of the hereinvillustrated example, these preformed slabs of sheet material are thendried out on a punch press, r by similar mechanism, or cut or punchedout by hand, to provide a number of discs having the diameter of theabrasive grinding wheel i shown iii-Figure 1. The arbor hole 5 isusually punched out at the same time. The punched out pieces of slabmaterial are ready for use in forming the desired abrasive article.

Reference is made to the drawings which depict an abrasive wheel 4,formed from a single disc-shaped segment of the slab material and havinga centrally positioned mounting arbor 5. As Figures 2 and 3 show, thissingle disc of initially compressed slab material consists of a'numberof layers of abrasive-included, felted fibrous sheet material 6 whichhave been adhesively coated with a thin layer of water-miscible phenolicresin composition 1. The single piece of slab material is placed on ahot press and subjected to a pressure of about 2000 pounds per squareinch at 260 F. for fifteen minutes to form the abrasive grinding wheel.The hot'pressed wheel is removed from the press, placed in an oven andbaked at about 260 F. for approximately ten hours to complete the curingof the adhesive. The article is then pressed and edged according tostandard practices whereupon it is ready for use. When only a singledisc-shaped piece of slab material is used the resulting abrasive Wheelis usually approximately 1A" thick.

Thicker wheels are formed by superimposing one or more additional piecesof slab material one on the other and hot pressing the several pieces ofslab material to combine them and compress the material to the desiredshape and density. In hot pressing wheels having a thickness of morethan 1A", the same temperature and pressure are used as for the thinnerWheels, the period of the hot-press cure being determined by allowing 15minutes for the rst 1A #thickness plus 5 more minutes for eachadditional 1A," thickness.

Improved methods of performing the hot pressing operation have beendevised for the making of abrasive articles of the herein describedtype; these improved methods are more fully set forth and described incopending application Serial No. 542,567 flled June 28, 1944, issued onJune 19, 1945, as U. S. Patent No. 2,378,386. These improved hotpressing operations are not only applicable to carrying out the presentinvention, in fact they constitute the preferred method of obtainingIthe flnal consolidation and formation of the abrasive article. Briefly,the pieces of slab material from which the grinding wheel or otherabrasive shape is to be formed are placed between two layers of heavycloth which have been previously saturated with water and the excesswater removed as by squeezing. A suitable fabric is heavy coarsely wovencanvas or duck, although other woven or felted materials suitablydampened can be used. By the use of these cloth layers between thehot-press platens and the piece or pieces of slab material constitutingthe abrasive article being formed, a more uniform abrasive body isobtained as is more fully explained in the aforementioned pendingapplication. Abrasive articles made by this latter metho-d, followingthe hot-pressing operation, are likewise subjected to an oven curesimilar to that set forth above.

Figure 3 which is highly enlarged, shows in detail the nature of thestructure of an abrasive grinding wheel as made above, using a singlepreviously cold pressed piece of slab material, It particularly showsthe manner in which the abrasive-included, felted fibrous sheets 6making up the wheel are substantially free from the laminating adhesivel which by reason of its non-penetrative properties has not penetratedthe fibrous structure to any appreciable degree, The small amount ofpenetration 8 shown adjacent the surfaces of the fibrous sheets servesto hold the sheet material strongly together without separation in useand furthermore produces in the wheel a somewhat harder and more rigidcondition which promotes a much faster cutting action and less wheelwear in use so as to increase the efiiciency of the wheel cutting ratebeyond that obtained using more resilient types of combining adhesives.At the same time the restrictionof that penetration from the greaterpart of the` fibrous structure serves to retain in the abrasive body theproperty of soft cutting and polishing action so desirable in such typewheels. v

It has been found that the character of `the abrasive articles producedby the herein-dei scribed process, as for example the grade of hardness,can be altered by variations in the quantity and character of theadhesive binder employed in making the abrasive-containing, fibroussheet material, and particularly by the herein-described choice ofauxiliary or supplemental adhesive substance which is admixed with the.sheet material as a size thereto. It is desirable that the adhesivesselected for making the aforesaid articles do not smear during grindingoperations. This is especially true in polishing wheels and deviceswhere smearing of the bond tends to produce a hot cutting or burningaction which is ruinous to the finish being produced.

The herein-described invention offers numerous improvements oradvantages over the prior art. It provides an abrasive article of thebonded type which combines an unusually high amount of material removalin grinding operations without a correspondingly high amount of wheelremoval together with a highly satisfactory polishing action;A As ademonstration of the manner in which the present use of water-misciblephenolic combining compositions of the herein-described type functionsin the abrasive product made in accordance herewith, grinding tests werecarried out on the grinding of steel using wheels employingwater-miscible phenolic resin compositions as the combining adhesive andsimilar tests made using wheels in which the combining adhesive was anordinary solution of a phenolic resin in an organic solvent. Thecomparative figures showed that wheels made with the herein-describedtype of combining adhesive removed more than 20% maalmost 50% less wheelloss than in the case ofk the latter type wheell l The articles of thepresent invention not only r1" are capable of grinding with a relativelyhigh rate of stock removal from rthe material being ground but at thesame time produce a surface finish equal to that obtained by an ordinarybonded abrasive article employing abrasive particles several gritssmaller. `Abrasive products made as herein-described cut both efcientlyand effectively With accompanying polishing action and are capable ofhigh operating speeds Without chattering, operating smoothly to removeburrs and produce very high finish on metal castings.

It is theorized that the soft cutting action ofY such abrasive articlesis the result of the abrasive grains being cushioned by the surroundingfelted bers and binder so as to prevent gouging and scratching and toprovide the abrasive grains With a yielding background by which they arecaused to maintain individually more eifective contact with the Work andat the same time absorb and take up inequalities `of the surface so asnot to marl or scratch the surface being nished,

Although certain specific conditions have been set forth for the examplegiven it Will be understood that the invention is not limited to theconditions therein described. Generally speakingit has been founddesirable to compress the articles under pressures of the order of 2,000to 4,000

pounds per square inch. The length of time that the article is subjectedto heat andv pressure is determined to some extent by the size of thearticle being formed but is usually in the range of 1-5`to 30`minutes.Likewise articles in different grades can be made by varying the type ofnbrous sheet material employed and the type and amount of adhesiveapplied thereto as a size.

a In, the specification and claims, where reference is made to anon-penetrative phenolic resin, the termis meant to include a phenolicresin which when applied as a sizing coating to the at face of a Ysheetof abrasive-included felted fibrous web material of the herein-describedtype, and that sheet is compacted with other sheets of similarly sizedfelted fibrous, abrasive-containing material, andthe assembly subjectedto the heat and/or pressure required to mature the resin, the resinsized coating on the felted sheet material will not penetrate theibrous` layers and impregnate the individualfbers of the fibrous sheetmaterial to such an extent that the iibers of the fibrous structure arerendered brittle and lacking in resilience; an abrasive article sofabricated, as a result of the lack of absorption of the resin into thefibers thereof, will be resilient and flexible and will cut with asoftness of action, that is, with an auxiliary polishing action, of theherein-described type. Y

One means of determining the efficacy of any particular resin for use asthe combining adhesive in practice of the present invention is to applya small arnouru-l of the proposed resin adhesive composition having aviscosity of 320 poises at 81 F. as measured on the Maclifiichael Visconsimeter (which viscosity has -been found to be satisfactory for useherein as the combining adhesive) to the surface of apiece of highlybibulous paper as, for example, ordinary unsized blotting paper, of.045"V in thickness. If the resinous material ofthe aforesaid viscositysoalss intoand penetrates the paper to the extent that it stainsy theVopposite side of the paper in less than one-hour, it is not consideredto be a nonpenetrative resin Within the intended meaning of the term. A.satisfactory non-penetrative a resin of the type herein employed, Whenreduced` to the Yaforernentionedil viscosityl and ap,-

plied to bibulous paper of the described type, will not penetrate thepaper to the extent of staining theA opposite side of the paper after aperiod of one hour and I prefer to employ resins which Will notpenetrate the paper, under the conditions specied, after a period ofseveral hours.

Having described and set forth the invention in detail the scope of theinvention is not to be confined other thanby the appended claims.

le claim:

l'. An abrasive article ofmanufacture comprising a plurality of layersof abrasive-included felted, fibrous sheet material, the major portionof the abrasive content ybeing distributed internally of; the fibroussheet material, said layers, of fibrous sheet material being adhesivelycombined in superimposed relation by means of an adhesive bindercomprising a phenolic resin which is substantially non-penetrative ofsaid fibrous sheet material.

2. An abrasive article of manufacture comprising a pluralityy of layersof abrasiveincluded felted, fibrous sheet material, the major portion ofthe abrasive content being distributed internally of the fibrous sheetmaterial, said layers of brous sheet material being adhesively combinedin superimposed relation by means of an adhesive binder comprising aphenolic resin and an inorganic fillelysaid phenolic resin beingsubstantially non-penetrative of said fibrous sheet material.

3. An abrasive article of manufacture com-1 prising a plurality oflayers of abrasive-includedfelted, fibrous-sheet material, the maiorportion of the abrasive content being distributed internally. ofjthefibrous sheet material, said layers of fibrous sheet material beingadhesively combined invsuperimposed relation luy-meansy of an adhesivebinder comprising a` phenolic resin and a cryolite filler, said phenolicresin being substantially non-penetrativev of said brous sheet material.

4'. A method of making bonded abrasive articles which comprises applyinga Coating of a nonpenet'rative phenolic resin adhesive composition to.the-V surface of an abrasive-included felted brous-Web material having amajor portion of the abrasive content distributed internallyl throughoutsaidl fibrousfsheet material, said adhesive composition beingsubstantially nonpenetrative of said fibrous sheet material, as-

sembling a.- plurality of sheets of saideadhesivelycoatedweb materialinl-superimposedrelation and compressing the saine, and heating to curethe resin.

5. A methodof making bonded abrasive articlesrwhichl comprises applyinga coating of a WaterV dispersion of a phenolic resin to the sur.- faceof an abrasive-included felted, fibrous web material havinga majorportion of. the abrasive contentl distributed internally throughout saidfibrous sheet material, said phenolic resin. dispersion beingsubstantially non-`penetrative of saidflbrous sheet material, assemblinga plurality of sheets of said adhesively-coated web mate-A rialinsuperimposed relation andcompressingthe same; and heating to cure theresin.

6. AV method of makingbonded abrasive articles which comprises applyinga coating of an adhesive` comprising a, Water dispersed, phenolic resin`and an inorganic filler to-the surface of an abrasiveincludedfelted,iibrous web material having a major portion of the abrasive contentdistributedinternally thereof, assembling a plurality, of, sheetsv ofsaid adhesively-coated Web material in superimposed relation andcompressing the same, and heating to cure the resin.

'7. A method of making bondedabrasive articles which comprises applyinga coating of an adhesive comprising a Water dispersed, phenolic resinand a cryolite iiller to the surface of an abrasive-included felted,brous web material having a major portion of the abrasive contentdistributed internally thereof, assembling a plurality of sheets of saidadhesively coated web material in superimposed relation and compressingthe same, and heating to cure the resin.

8. A method of making bonded abrasive articles which comprises applyinga coating of a nonpenetrative adhesive composition comprising awater-miscible phenolic resin to the surface of an abrasive-includedfelted, fibrous web material having a major portion of the abrasivecontent distributed internally throughout said brous sheet material,said adhesive composition being substantially non-penetrative of saidfibrous 14 sheet material, assembling a plurality of sheets of saidadhesively-coated web material in superimposed relation and compressingthe same, and heating to cure the resin.

9. A method of making bonded abrasive articles Which comprises applyinga coating of a nonpenetrative adhesive compositionA comprising a

